Sea level rise may up risk of devastating tsunamis

Even minor rise in sea levels due to climate change can increase the risk of potentially devastating tsunamis around the world, a study has warned.

The threat of rising sea levels to coastal cities and communities throughout the world is well known, but new findings show the likely increase of flooding farther inland from tsunamis following earthquakes.

For example, the tsunami that devasted a portion of northern Japan after the 2011 Tohoku-Oki earthquake also caused a nuclear plant to melt down and spread radioactive contamination.

"Our research shows that sea-level rise can significantly increase the tsunami hazard, which means that smaller tsunamis in the future can have the same adverse impacts as big tsunamis would today," Robert Weiss, an associate professor at Virginia Tech in the US.

For the study published in the journal Science Advances, researchers created computer-simulated tsunamis at current sea level and with sea-level increases of 1.5 feet and 3 feet in the Chinese territory of Macau.

Macau is a densely populated coastal region located in South China that is generally safe from current tsunami risks.

At current sea level, an earthquake would need to tip past a magnitude of 8.8 to cause widespread tsunami inundation in Macau. But with the simulated sea-level rises, the results surprised the team.

The sea-level rise dramatically increased the frequency of tsunami-induced flooding by 1.2 to 2.4 times for the 1.5-foot increase and from 1.5 to 4.7 times for the three-foot increase.

"We found that the increased inundation frequency was contributed by earthquakes of smaller magnitudes, which posed no threat at current sea level, but could cause significant inundation at higher sea-level conditions," said Lin Lin Li, a senior research fellow at the Earth Observatory of Singapore.

"We produced a series of tsunami inundation maps for Macau using more than 5,000 tsunami simulations generated from synthetic earthquakes prepared for the Manila Trench," said Adam Switzer, an associate professor at Earth Observatory of Singapore.

It is estimated that sea levels in the Macau region will increase by 1.5 feet by 2060 and 3 feet by 2100.

The hazard of large tsunamis in the South China Sea region primarily comes from the Manila Trench, a megathrust system that stretches from offshore Luzon in the Philippines to southern Taiwan.

The Manila Trench megathrust has not experienced an earthquake larger than a magnitude 7.8 since the 1560s.

Yet, researchers cautioned that the region shares many of the characteristics of the source areas that resulted in the 2004 Sumatra-Andaman earthquake, as well as the 2011 earthquake in northern Japan, both causing massive loss of life.

These increased dangers from tsunamis build on already known difficulties facing coastal communities worldwide: The gradual loss of land directly near coasts and increased chances of flooding even during high tides, as sea levels increase as the Earth warms.